In the prior art the powertrain control in a motor vehicle takes place by interpreting the driver's command, imparted by means of the accelerator pedal, and translating this command into a request signal for a drive torque delivered by the engine itself as a function of the speed of rotation of the drive shaft. The power or the torque which is effectively applied to the drive wheels depends not only on the drive torque thus delivered from the engine, but also on the gear ratio selected at the gearbox.
In a motor vehicle with a servo-assisted gearbox and architecture of manual type the commands imparted by the driver through the accelerator pedal, and possibly also the brake pedal, and the commands (via push button or lever) for selection of the transmission ratio, are interpreted by a gear management unit for selection of the transmission ratio and actuation of the clutch.
In International Patent Application WO 01/02210 in the name of the same Applicant, there is described a powertrain control system for a motor vehicle which makes it possible to manage the engine with a greater degree of freedom than with conventional systems. This control system is applied to the integrated traction control of a motor vehicle provided with a gearbox having servo-assisted gears including an input shaft connectable to the drive shaft by means of a servo-controlled clutch, and in which respective electrically controlled actuators are associated with the gearbox and the clutch.
In motor vehicles provided with gearboxes of the servo-assisted or ‘robotised’ type, traction control, i.e. control of the power or torque applied to the drive wheels and exchanged with the ground, is the combined result of the command imparted by the driver via the accelerator pedal and the gear ratio or ‘speed’ selected by the driver. In the case of drivers who are not particularly expert, traction control, i.e. control of the torque effectively applied to the drive wheels and exchanged with the ground, is not in general optimal in such motor vehicles.
An integrated powertrain control system has therefore been designed, based on the idea of controlling via the accelerator pedal, not the drive torque delivered by the propulsion unit, but rather directly the power applied to the drive wheels of the vehicle, exploiting for this purpose the automatic management of the gearbox. In other words, the driver does not just control the engine via the accelerator pedal, but rather also manages the dynamics of movement of the vehicle.
Even in the most highly developed prior art mentioned above, it happens that the integrated engine/gearbox control essentially consists in putting the well known strategies of ‘engine control’ and ‘gearbox control’ side by side, each of these being separately managed by an associated electronic control unit designed separately.
The said architecture presents various disadvantages.
In a system with two separate control units, respectively for the engine and the gearbox, the torque release and reinstatement operations are performed in a non-optimised manner. In fact, the engine responds to the torque demands communicated by the gearbox control unit without knowing the type of manoeuvre required (dynamics, times, jerk, . . . ) with negative effects on the speed and precision of response of the engine itself. In the same way the gearbox control unit sets the torque release and reinstatement ramps without knowing the real requirements or constraints of the engine (warm up, maximum real power, additional resistant loads, . . . ), which therefore is not always able to satisfy the requirements of the gearbox.
Moreover, in a motor vehicle provided with a plurality of on board accessory systems for automatic traction control, for the aid of the driver, these can present torque demands to the engine simultaneously and in conflict with one another.
For example, a situation of this type occurs when during starting from rest on slippery surfaces such as icy ground.
In this case, the acceleration command imparted by the driver through the accelerator pedal has superimposed thereon an engine torque reduction command from an anti-slip system (ASR) of the vehicle.
The ASR system, in reducing the engine torque demand with respect to that required by the driver, acts in parallel with the gear control system, and in particular with reference to a clutch-engaged condition. This, however, does not represent a real operative condition when starting from rest, in which the torque delivered by the engine is modulated by the clutch which is not completely engaged.
By undertaking a dialogue with the engine control unit, the gear control system reacts to the torque reduction command imparted by the ASR system, controlling rapid engagement of the clutch in such a manner that by the effect of the coupling of the propulsion unit with the transmission, the engine is the only ‘actuator’ able to modulate the torque at the wheels and therefore to satisfy the requirements of the ASR system. It is evident in this case that the first action performed in response to the request from the ASR system goes in the opposite direction from the objective of reducing the traction torque at the wheels in the shortest time.